1. Field of the Invention
This invention relates to processes for preparing polyimides and certain polyimides obtained thereby and more particularly to such processes and polyimides starting from bis-maleimides.
2. Prior Art
The inventor is aware of no prior art where an adduct is made from a pre-synthesized, completely cyclized bis-maleimide of the formula: ##STR1## wherein Ar is a divalent aromatic organic radical,
Ar' is a tetravalent aromatic organic radical, the four carbonyl groups being attached directly to separate carbon atoms and each pair of carbonyl groups being attached to adjacent carbon atoms in the Ar' radical, and PA1 n is 0 or a positive integer of 1 to 20, and a cyclic diene of the formula: ##STR2## wherein Y is --O--, --S--, or ##STR3## and EACH R.sub.1 is hydrogen or an aliphatic hydrocarbon of 1 to 4 carbon atoms with the proviso that the sum of the R.sub.1 is no greater than 4 carbon atoms, PA1 Ar' is a tetravalent aromatic organic radical, the four carbonyl groups being attached directly to separate carbon atoms and each pair of carbonyl groups being attached to adjacent carbon atoms in the Ar' radical, and PA1 n is 0 or a positive integer of 1 to 20. PA1 each R.sub.1 is hydrogen or an aliphatic hydrocarbon of 1 to 4 carbon atoms with the proviso that the sum of the R.sub.1 s is no greater than 4 carbon atoms, and PA1 m is a positive integer of 1 to 2, PA1 Ar' is a tetravalent aromatic organic radical, the four carbonyl groups being attached directly to separate carbon atoms and each pair of carbonyl groups being attached to adjacent carbon atoms in the Ar' radical, and PA1 n is 0 or a positive integer of 1 to 20.
And then reversing the adduct to increase the molecular weight of the product. The only prior art known to the inventor are polyimides whose end-groups are derived from the endomethylene phthalic anhydrides. These prior art adducts are cured directly, presumably by the formation of terminal maleimide groups. Such polyimides are shown in U.S. Pat. No. 3,738,969, issued June 12, 1973, to Fred F. Holub and Denis R. Pauze.
Other prior art references of interest are U.S. Pat. Nos. 3,748,310 and 3,748,311, all issued July 24, 1973, to Eugene A. Barns and Robert J. Jones; U.S. Pat. No. 3,632,428, issued Jan. 4, 1972, to Hyman R. Lubowitz et al; U.S. Pat. No. 3,699,074, issued Oct. 17, 1972, to Hyman R. Lubowitz et al and U.S. Pat. No. 3,763,101, issued Oct. 2, 1973 to Robert J. Jones and Eugene A. Burns.
There appears to be no prior art teaching adducts from cyclic pentadienes or cyclic dienes, containing oxygen or sulfur as the hetero atoms in the five membered ring, useful for the purposes of this invention.